Wargaming EU Community Coordinator MrConway made an announcement here: “Update 0.5.5 brings new file compression system into WoWS. Unlike the previous versions, the new file compression format is not compatible with usual compression utilities. To allow mod makers to still be able to use game files, we are sharing an unpacking utility. To give mod makers time to prepare, we are already sharing this utility with you now.”

If no filtering is given, all contents are to be processed (unpacked or listed).

Filter options may be used more than once – each time adding a new rule into a filter chain.
Rules are applied in the same order they are given in a command line. First rule sets the head of a filtering chain: either exclude everything, or include everything for -I and -X options respectively.

Examples:

List all the contents of res_packages:

wowsunpack.exe -l res_packages > content.txt

Unpack all the contents of res_packages into default “unpacked” folder:

wowsunpack.exe -x res_packages

Unpack all the contents of res_packages into “my_unpack” folder:

wowsunpack.exe -x res_packages -o my_unpack

Unpack only *.swf files from res_packages:

wowsunpack.exe -x -I *.swf res_packages

Same as above, but more explicit:

wowsunpack.exe -x -X * -I *.swf res_packages

Unpack only *.swf files except main_scene swf files:

wowsunpack.exe -x -I .swf -X *main_scene res_packages

Note: When the mod is done, it is not necessary to pack the mod files – To make a mod work, all that is needed is putting the modified file(s) to res_mods/0.5.5.x directory